The present invention relates to a method for fabricating a T-shaped electrode and metal layer having a low resistance, and more particularly, to a method for fabricating a T-shaped gate electrode and metal layer having a low resistance in which the T-shaped gate electrode is formed in self-alignment using a fine photoresist pattern, and the metal layer having a low resistance is formed on a fine gate electrode in self-alignment using the method for forming the T-shaped gate electrode, thereby simplifying the fabricating process and increasing mass productivity.
For the purpose of fabricating an ultra-high speed integrated circuit using a metal semiconductor field effect transistor (MESFET), the MESFET should have many various high frequency characteristics. Generally, a MESFET formed using GaAs has a cutoff frequency over 25 GHz in a device having a gate length of below 0.5 .mu.m. Its frequency characteristic becomes higher as the gate width is decreased. However, the reduction of the gate width decreases the cross-section area of the gate, thus deteriorating noise characteristics. Accordingly, several methods are proposed, which are for reducing the gate length and, at the same time, decreasing the gate resistance using a T-shaped gate electrode. According to the first method for forming the T-shaped gate electrode, a T-shaped resist pattern is formed by using electron-beam lithography, and then a metal is deposited thereon and lifted off. By the second method, a fine resist groove is formed through lithography, and another resist pattern having an open portion wider than the groove is formed, to form a T-shaped groove. Then, the T-shaped gate electrode is formed using the resist groove and upper resist.
According to the third method for forming the T-shaped gate electrode, a temporary gate is formed using a photoresist, a fine groove is formed by using this temporary gate and a resist pattern having a large width is formed on the groove. Then, a metal having a low resistance is deposited over the resist pattern, and then is lifted off, thereby forming the T-shaped gate electrode. The fourth method is performed in a manner that a gate is formed, a planarizing layer is formed thereon and etched to expose the gate, and then a resist pattern having a width wider than that of the gate is formed over the gate. A metal is deposited thereon and is then lifted off, thereby forming the T-shaped gate electrode.
However, the first method requires very expensive equipment for E-beam lithography and second method requires two lithographic process sequences, reducing the productivity thereof. Also, in case of the third and fourth methods, the gate electrode is easily formed due to the misalignment of the top metal layer, and requires two lithographic process sequences.